Solar energy has not, as yet, approached its potential for use because of the costs associated with capturing it in a widely useful form. While a type of solar panels can warm water and some architectural constructions capture the sun's heat to warm a space, these capture devices are rather limited in their diversity. Another type of solar panel is adapted to convert light into electricity, but the capital cost of these has prevented their widespread use.
Often a desire to warm an article, a mass of material, or a place is linked to a need to apply other forms of energy to it as well. For example one might want to heat the interior of a building and also supply moving air and lighting, and perhaps electricity in a conventionally usable voltage and frequency. One might want to heat a greenhouse, fan it and light it, or warm a swimming pool and purify the water within it, or dry agricultural produce, laundry, or the like with a combination of heat and moving air. These demands can be met from utilities such as reticulated gas or electricity but they tend to be wasteful of limited supplies in that often only a small increment of heating above ambient is required and there may be alternative sources available for energy which need not be taken from the reticulated supply.
Considering swimming pools as a particular example, there is a need for extension of the duration through a year that a swimming pool can be enjoyed; at present the winter months tend to provide insufficient warming and hence the pool is little used in winter. Domestic swimming pools have the clear primary function of providing leisure activities and also providing a means for exercising. They are also valuable as a reserve of water for fire fighting purposes. Maintenance of the pool for fire fighting depends on its appreciation for its other functions.
Another focus of attention is solar energy. At the time of writing, it is expensive in terms of capital cost to convert sunlight into electricity, largely because of the manufacturing processes involved in making an efficient solar cell out of crystalline (or amorphous) silicon or other scarce semiconductors such as gallium. While some solar cell efficiencies are of the order of 20% these are accompanied by higher capital costs. Much research is being invested in more efficient yet cheap solar cells, or (ideally) a cheap, spray-on or otherwise conformable coating which provides an electric output. Furthermore solar energy is far less effective on a cloudy day, or at night. Yet the benefits of using solar energy are well worth the effort.
Improving the cost-effectiveness of the capture of power from solar radiation should make non-renewable resources last longer and minimise the destruction of scenic areas for hydro-electric dams or wind farms or the like. An estimate of national power consumption in New Zealand for domestic water heating purposes alone is of the order of 40% of the total electricity generated. Thus a widely applied invention which minimises this particular type of consumption is likely to be useful, also because locally generated power would not incur the additional 10-20% transmission losses that occur when high-voltage current is sent over a considerable distance. New Zealand is nearing the end of its prospects for economical hydro-electric generation (85% of generating capacity is hydro-electric and the average cost of generation is about 3 c per unit). The cost of building a thermal power station is about $4000 per kW of capacity. Windmills are slightly cheaper. There is a growing need for alternative sources, preferably avoiding use of fossil fuels which are non-renewable and add to atmospheric carbon dioxide. FIG. 14 shows examples of various options of absorbing surface as seen from the mirror side.